PPS resin has good resistance to heat, flame and chemicals, and has high rigidity. It is a very useful engineering plastic. However, it has a drawback: low impact resistance. Accordingly, resin compositions which exhibit the excellent properties of PPS while minimizing its drawbacks have been proposed in the past.
For instance, Japanese Patent Application Laid-Open No. 156561/75 discloses a resin composition comprising polyphenylene ether (hereinafter referred to as PPE) and PPS in which PPS is added to improve moldability and fire-resistance of PPE.
Japanese Patent Application Laid-Open No. 69255/78 discloses a polyphenylene ether resin composition containing PPS and polyamide. This intends to improve brittleness of PPS.
Further, Japanese Patent Application Laid-Open No. 213758/84 proposes a resin composition in which a polyamide resin and an epoxy resin are admixed to a blend of PPS and PPE in order to improve compatibility between PPS and PPE.
In the case where PPE and polyamide are blended with PPS to improve the brittleness of PPS as mentioned above, the simply-mixed resins are brittle and the surface appearance is not excellent because PPS and PPE are intrinsically incompatible with each other. In the case where the compatibility between PPS and PPE is improved by adding polyamide and an epoxy resin, the epoxy reacts with polyamide and PPS, which results in a problem of unstable melt flow properties. Also, when polyamide is admixed with PPS, compatibility between PPS and polyamide is insufficient, so that improvement of the brittleness of PPS is insufficient and, moreover, a new problem, delamination, takes place.
In the above circumstances, the present inventors disclosed, in Japanese Patent Application Laid-Open 20355/91, that a certain type of compound such as citric acid is added to a PPS/PPE/polyamide system to thereby specify the dispersion state of each resin and, accordingly, it is possible to improve the surface appearance, brittleness and heat resistance of a PPS resin composition.
Meanwhile, the present inventors also disclosed, in Japanese Patent Application Laid-Open 20356/91, that the brittleness to impact is improved by adding an unsaturated monomer and/or a polymer, each having an epoxy and/or oxazolinyl group to a PPS/PPE resin composition.